The injection molding machine using servo motors for drive sources of each process has been popularly used now. However, even in such event, servo motors are used at most for drive sources, such as (1) injection into die cavities of weighed resin, (2) weighing of blended resin, (3) opening and closing of dies, (4) gate cutting, etc., and there has been no case in which servo motors are used in the product eject process. This is because as shown in FIG. 21, the location of screw mechanism for gate cutting is concentrated with an extremely large number of mechanisms, and an air cylinder has conventionally been used for drive sources of the product eject pin for a device that can be barely contained in this portion.
First Problem
As observed recently, when the high cycle of injection molding machines advances gradually, the time for removing ejected products causes problems. An attempt to shorten time naturally requires accurate response at this portion. However, the air cylinder has limitations in response speed as well as variations in response timing, and the shortening and improvement in accuracy in product removal from the air cylinder have reached their limits.
To show one example, assume that the desired production cycle time per product is 3 seconds, the time assigned from eject to product removal is 0.12-0.15 second, whereas when an air cylinder is used, 0.2 second is required, and approaches by the air cylinder become extremely difficult.
In addition, because there are variations in repetitive response accuracy of the air cylinder on order of 0.01 second, an allowance from 0.02-0.05 second must be provided for timing of product removal carried out by a product removing equipment (not illustrated), and when still higher cycle is aimed at, the air cylinder has a problem of large time loss in shortening of the overall time.
Second Problem
In the electrically-operated injection molding machine of the conventional example using servo motors, each servo motor is feedback controlled in each process based on the program data for servo control. This takes in the data from the encoder equipped to the relevant servo motor into CPU for arithmetic, and the position, speed, torque, etc. are feedback controlled as specified in the program.
However, this kind of control method is an indirect control method of the position, speed, torque, etc. via the encoder equipped to the servo motor, and has been unable to directly detect injection pressure, weighed resin pressure, and die clamping force, etc. actually applied to the screw and dies and to feedback control based on the actually detected data. That is, because it was unable to find any place to install a pressure sensor for directly detecting the die clamping force applied to the dies, it was unable to directly detect the die clamping force and carry out feedback control.
Third Problem
In the electrically-operated injection molding machine which uses many servo motors, using one servo motor for one operating mechanism results in too many servo motors, causing disadvantages of not only enormous equipment costs but also complicated control.
Fourth Problem
Recently, the digital technique has been popularized in various fields including data processing, images, and music, and as a natural consequence, for example, CD, MD, DVD, and other digital substrates have been put into practical use. In particular, in PVD substrates, it is required to transfer super fine protrusions and recessions formed on dies accurately to moldings, and hydraulically-controlled conventional injection molding machines are no longer able to satisfy the requirements.
Consequently, injection molding machines which use many servo motors as described above, though partly, have been developed. And as this kind of increased precision of injection moldings advances, not only injection molding machines but also injection molding methods have continuously evolved. In this kind of injection molding machines, the following will govern the substrate accuracy.
For example, taking molding of optical disk substrates for example, warpage of moldings, adhesion of foreign matter, void, discoloration by gas, molding cycle, etc. constitute extremely important factors, but above all, the biggest problems are (1) super fine pitch, (2) pit transferability of depth, (3) realization of double refraction of 50 nm or less, and it is possible to suppress double refraction by alleviating (photoelasticity coefficient.times.main stress difference [=shear stress+thermal stress]).
Now in substrate molding, (1) microvoids and (2) micro flowmarks can be mentioned for factors that check transferability of fine protrusions and recesses.
That is, when resin flows along fine protrusions and recessions, air entrapping phenomena occurs in the resin flow in the front and the rear of the wall of fine protrusions and recessions, and fine air pools are formed. This fine air pool causes degraded transferability, and the countermeasure is to suppress resin solidification by high-speed filling as much as possible and to complete filling. However, this was insufficient. by conventional injection molding method. In addition, timing of injection compression is an important factor.
The foregoing description can be summarized as follows. In these several years, practical application and its development of digital substrates have been remarkable, and new deployment of injection molding machines and injection molding technique has been called for. At the same time, the demand for still higher cycle of forming speed has been exceptional, and for a solution, adoption of the servomechanism of all the drive units has been promoted.
(1) It is the screw mechanism for ejection for removing moldings from dies and direct detection of resin filling pressure and clamping force to dies at the die portion that constitute bottlenecks in adopting servomechanism. Even if pressure sensors are intended to be installed to the movable die side for directly detecting resin filling pressure or die clamping force, there is a limitation in space, and even when the pressure sensor is installed on the movable die side, there is a restriction in that the screw mechanism for ejection is unable to be installed unless some special construction is adopted, and in addition, it is also a limit in space.
(2) The adoption of servomechanism naturally means feedback control, but because in conventional cases, actual resin filling pressure and die clamping force were unable to be detected, they must be processed by feedback control using the data from the encoder attached to the servo motor.
(3) The reduced number of servo motors is quoted as one of the requirements together with adoption of servomechanism.
(4) Another object of requirements for adoption of servomechanism lies in improvement of transferability of super fine protrusions and recessions for, for example, optical digital substrates.